1. Field of the Invention
The present invention relates generally to a serial printer for carrying out uni- or bi-directional printing with a printing head mounted on a carriage and, more particularly, to a printing controller for controlling the initial position of printing.
2. Description of the Prior Art
In serial printers for carrying out printing while reciprocating a carriage by a motor via a transmitting means, the initial printing position has been controlled by using a position signal emitted from a carriage position detector and a timing signal for detecting the rotational position of the motor.
That is, a judgment has been made as to whether or not the carriage is located at a home position (a reference position for the initiation of printing) on the basis of the position detection signal detected by the carriage position detector, and a printing initiation signal has been produced by a timing signal which is first fed to the carriage upon its leaving the home position for the initiation of printing.
However, such conventional serial printers have had the following disadvantage which must be overcome.
That is, there has generally been a need to produce timing signals in at least a half-dot unit, which has further required a high resolving power and, hence, to detect the signals at a high-speed stage of, e.g., a driving shaft of a carriage driving motor. Turning on the other hand to the position detecting signal for detecting the position of the carriage, the movement of said carriage has been detected by using photo-interrupters, lead switches, limit switches and the like. Since the carriage is driven via a transmitting means such as gears and a belt, however, there is a variation in the number of timing signals from the position detection signal for an "on" state to the timing signal for the initiation of printing due to a backlash of a gear train, a flexing of a carriage driving belt and pulley shafts resulting from a fluctuation of the tension of said belt, a dimensional change of components caused by their temperature dependencies, etc. A problem with the prior art has been that such a variation in the number of timing pulses gives rise to a variation in the initial printing position, resulting in irregular printing.